Mazda MX-5 1990 Workshop Manual page 165

TROUBLESHOOTING GUIDE
STEP INSPECTION
4
5
6 Check if approx. 12V exists at injector connector
(W/R) wire with ignition switch ON
7 Connect diagnosis connector terminals F/P and
GND with jumper wire and check for correct fuel
line pressure with ignition switch ON
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Fuel Line pressure:
265-314 kPa (2.7-3.2 kg/cm
2
,
38-46 psi)
~
~I~
GND F/P
8 Check for correct engine compression
L7
page 8-10
Engine compression: 1,324-932 kPa
(13.5-9.5 kg/cm
2
,
192-135 psi) • 300 rpm
9 Check if spark plugs are OK
WEAR AND CARBON BUILDUP
PLUG GAP
1.0-1.1mm
(0.039-0.043 in)
DAMAGE AND
DETERIORATION
DAMAGE
10 Try known good ECU and check if condition
improves
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ACTION
Yes Check continuity of fuel pump
No Check circuit opening relay
Yes Go to Step 7
No Go to Step 6
Yes Check ECU terminals 2A, 2U and 2V
voltages
No Check for open circuit in wiring be-
tween main relay and injector
Yes Go to next step
No
Low pressure
Check fuel line pressure while pinching
fuel return hose
¢ If fuel line pressure quickly in-
creases, check pressure regulator
¢
If fuel line pressure gradually in-
creases, check for clogging be-
tween fuel pump and pressure
regulator
If not clogged, check fuel pump
maximum pressure
Yes Go to next step
No
Check engine condition
• Worn piston, piston rings or cylinder
wall
• Defective cylinder head gasket
• Distorted cylinder head
• Improper valve seating
• Valve sticking in guide
Yes Go to next step
No
Repair, clean, or replace
F
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F-10a
IT
page 8-10
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05UOFX-019
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